This invention relates to waste treatment systems, and in particular, to a method for removing ammonia content from waste streams with a high ammonium-nitrogen concentration.
The supernatant from the anaerobic digestion of blended or secondary sludge contains high concentrations of ammonium that as a recycle stream to the influent of a wastewater treatment plant may account for as much as 25% of the nitrogen loading to the plant. In addition, this recycle stream typically does not contain the requisite carbon to nitrogen ratio (C/N) for nitrogen removal. However, removal of the nitrogen prior to reentering the treatment plant would reduce the main treatment plant's downstream nitrification and denitrification requirements and may provide additional options for treatment plant upgrades.
The removal of nitrogen from wastewater streams is a two step process. In the first step the oxidation of ammonium to nitrate (i.e. nitrification) is accomplished by the aerobic growth of chemolithotrophic, autotrophic bacteria in an aerobic environment. This first step results from two separate, sequential reactions. The first reaction in step one is the conversion of ammonium to nitrite as described by:NH4++2.457O2+6.716HCO3−0.114C5H7O2N+2.509NO2−+1.036H2O+6.513H2CO3 
This is carried out by ammonia oxidizing bacteria (AOB). The second reaction in step one is the conversion of nitrite to nitrate and is described by:NO2−+0.001NH4++0.014H2CO3+0.003HCO3−+0.339O20.006C5H7O2N+0.003H2O+1.348NO3−
This is carried out by nitrite oxidizing bacteria (NOB). The overall biochemical transformation is described by the following mass based stoichiometric equation, normalized to ammonium.NH4++3.30O2+6.708HCO3−0.129C5H7O2N+3.373NO3−+1.041H2O+6.463H2CO3 
In the second step organic carbonaceous matter (organics) is oxidized by the growth of heterotrophic bacteria utilizing nitrate as the terminal electron accepter (i.e. denitrification). The equation describing the biochemical transformation depends on the organic carbon source utilized. The following is the mass based stoichiometric equation, normalized with respect to nitrate, with the influent as the organic carbon source (Water Environment Federation 1998).NO−3+0.324C10H19O3N=0.226N2+0.710CO2+0.087H2O+0.027NH3+0.274OH−
Nitrification occurs only when the quantity of organic carbonaceous matter has been reduced according to the well-established criterion for the transition from oxidation of organics to nitrification, within the biofloc. However, typically, the centrate from the dewatering process does not contain a large quantity of organics and therefore the criterion to achieve nitrification is readily established. However, the low carbon to nitrogen ratio (C/N) resulting from the lack of organics means that denitrification will not proceed without a supplemental carbon source.